High-resolution neutron structure of nicotinamide adenine dinucleotide

The structure of the free-acid form of the coenzyme NAD(+) was determined a t 100 K from a single-crystal neutron experiment. NAD(+) is the oxidized fo rm of the coenzyme redox pair NAD(+)/NADH and plays an important role in th e catalysis of biological processes. The molecule crystallizes in space gro up P1 with one NAD(+) and four water molecules per unit cell. The structure is compared with the previous X-ray models of NAD(+) [Reddy et al. (1981), J. Am. Chem. Soc. 103, 907-914; Parthasarathy & Fridey (1984b), Science, 2 26, 969-971; Guillot et al. (2000), Acta Cryst. C56, 726-728]. The crystal packing and the hydrogen-bond pattern are discussed as well as four short C -H...O contacts involving the pyridine and adenine rings. The structure dis plays stereochemical distortions owing to the hydrogen bonding and crystal- packing constraints, reflecting the adaptability of the NAD(+) molecule in various chemical environments.